Authorization bypass via implicit nil queries

Improper nil handling in Ecto 2.2.0 allows remote attackers to make applications execute unintended database queries via crafted API fields. Ecto.Repo.Queryable.query_for_get_by converts a nil Repo.get_by clause into an is_nil predicate instead of rejecting the comparison, so attacker-controlled JSON null values can target records whose security-sensitive field, such as a token, is NULL. Exposure requires an application to pass remote input into Repo.get_by or Repo.get_by!, and resulting record access remains bounded by the application's query and authorization logic.